What is the role of the iris in vision?

What is the role of the iris in vision?

• A. It balances intraocular pressure.
• B. It produces aqueous humor.
• C. It controls the amount of light entering the eye by adjusting the pupil size.
• D. It changes the color of the iris.

Answer: (C)

Light levels vary; the iris acts like a diaphragm around the pupil, adjusting its size to control how much light reaches the retina. It contains circular smooth muscle that constricts the pupil and radial smooth muscle that dilates it. In bright conditions, the parasympathetic system activates the sphincter pupillae to narrow the pupil, limiting light and glare. In dim conditions, sympathetic signals widen the pupil via the dilator pupillae to let more light in. This dynamic adjustment helps optimize vision, protecting photoreceptors and aiding contrast and depth of field. The iris does not produce aqueous humor (that’s the ciliary body) and it doesn’t directly regulate intraocular pressure. Iris color is a fixed trait determined by pigment and isn’t a rapid determinant of light entry.

Light levels vary; the iris acts like a diaphragm around the pupil, adjusting its size to control how much light reaches the retina. It contains circular smooth muscle that constricts the pupil and radial smooth muscle that dilates it. In bright conditions, the parasympathetic system activates the sphincter pupillae to narrow the pupil, limiting light and glare. In dim conditions, sympathetic signals widen the pupil via the dilator pupillae to let more light in. This dynamic adjustment helps optimize vision, protecting photoreceptors and aiding contrast and depth of field. The iris does not produce aqueous humor (that’s the ciliary body) and it doesn’t directly regulate intraocular pressure. Iris color is a fixed trait determined by pigment and isn’t a rapid determinant of light entry.